Research: Babies breastfeed overnight to prevent siblings

Sleep – or more accurately, lack of – would easily rate among the top concerns for parents of newborns. But new research suggests babies wake at night out of more than just hunger. It is also a clever (and we’d say effective) way of preventing their parents from having more children, at least temporarily.

A Harvard University study suggests night-waking is a survival method for newborns – a ploy to stop their parents producing more offspring that would compete with them and ultimately reduce their chance of survival.

In the Troubled Sleep study, published in the Evolution, Medicine and Public Health Oxford Journals, researcher David Haig contends many babies who breastfeed overnight are trying to extend their mother’s postnatal infertility, or lactational amenorrhea.

The study says breastfeeding can act as a natural contraceptive, and historically it has been in the child’s best interests to delay the birth of a younger sibling that would share its parents’ resources and attention.

“Short delays until the birth of a younger (sibling) are associated with increased mortality of infants and toddlers, especially in environments of resource scarcity and rampant infectious disease,” the report says.

More frequent and intense suckling help prolong the onset of ovulation, the study says.

“Maternal fatigue can be seen as an integral part of an infant’s strategy to extend the (interbirth interval),” it says.

The study found night-time crying in breastfed babies increased in the second half of their first year before gradually improving. It also found weaned or bottle-fed infants woke less often than breastfed babies.